Field oriented control is a well-known instantaneous torque control method for AC motors. In this method, an integrator included in the automatic current regulator causes the deterioration of torque response due to the saturation of output voltage, and the inevitable shocks to torque response caused by switching from linear to over-modulation and single-pulse operation of the inverter. To solve these problems caused by an integrator, this paper proposes a novel torque control system without an integrator. In the proposed method, we focus on the relationship from the input voltage to the output torque, which can be expressed by a first-order differential equation (i.e., torque derivative equation); thus, the controlled plant can be regarded as consisting of a first-order differential equation and an integrator. Since the proposed method consistently controls the torque based on the torque derivative, the torque response can be specified to the time constant of the torque controller and the switching the control systems according to the operating conditions do not needed. This enables over-modulation and single-pulse driving while guaranteeing the performance of the torque response. The effectiveness of the proposed torque control system is experimentally demonstrated.

In this paper, a reference stator flux linkage calculation method is proposed for realizing maximum efficiency operation in direct-torque-controlled interior permanent magnet synchronous motor (IPMSM) drives. The proposed method is based on the solutions of a quartic equation, a motor model in the d-q rotating frame widely used for synchronous motor controllers, and a well-known equation for maximum efficiency operation. Therefore, the proposed method uses neither any approximation function nor any look-up table that depends on the parameters of the motor, which has to be created in advance. Simulation results validate that the proposed methods can achieve maximum efficiency operation in IPMSM drives.

For sensorless vector control of PMSM (Permanent Magnet Synchronous Machine), the effectiveness of a resonance controller is investigated to suppress velocity pulsation caused by periodic disturbance torque. The controller design method and stability analysis results are presented. The validity of the proposed design method and analysis results is confirmed by actual machine experiments.

Several torque ripple suppression methods have been proposed considering the nonlinearity of magnetization characteristics for interior permanent magnet synchronous motors (IPMSMs). These methods can be used even in conditions where magnetic saturation is significant. However, since the magnetization characteristics change depending on the magnet temperature and other factors, the effect of torque ripple suppression may deteriorate depending on the environmental temperature. This paper proposes a torque ripple suppression control that considers the nonlinearity of magnetic saturation and variation of magnetization characteristics depending on temperature. From the experimental results, the proposed method suppresses the 6th-order torque ripple by 86.3%, which is higher than the 65.0% obtained using the conventional method. In addition, experiments show that a linear approximation model that calculates magnetization characteristics at unmeasured temperatures from a few measurement points is effective.

Current control of three-phase AC motors with three-phase windings is generally performed via vector control. The basis of current control of motors with good characteristics entails obtaining a sinusoidal current with no ripple in steady state. However, in practice, current ripple often occurs due to inverter nonlinearity and other factors. Current ripple suppression is required to obtain the desired current response. This paper proposes a new current ripple suppression method using a D-matrix disturbance suppressor. The proposed disturbance suppressor has the following advantages. 1) It can be designed and implemented independently of the original current controller due to the structure of the two-degree-of-freedom control system. 2) It can selectively suppress current ripples based on the intensities of positive- and negative-phase current harmonics. 3) It has a high degree of freedom in configuration. 4) It is simple to design and implement.

Accurate geometry parameters of interior permanent magnet synchronous motors (IPMSMs) are required to analyze the characteristics of the motor via electromagnetic field analysis. However, in some cases, it may not be possible to fully disassemble the IPMSMs being evaluated, resulting in limited access to certain geometry parameters. This study investigates a method for estimating the geometry parameters of the IPMSMs using Bayesian optimization. The proposed method can estimate ten remaining geometry parameters that cannot be measured from the fourteen parameters and electrical parameters obtained without fully decomposing the motor. Since the composition of the magnets and other materials is unknown, the shape parameters obtained by the proposed method are slightly different from those obtained by actual shape measurements. However, the electrical characteristics are close to those of the actual machine. Even though torque was not used in the estimation, the error could be reduced from 18% to 3.6%.

Artificial intelligence (AI) translators have made remarkable progress in translation accuracy, resulting from the emergence of “generative AI. ” Doraemon is a fictional cat-like robot from the 22nd century, who brings various unknown tools out of his pockets. One of the tools is the universal translator “Honyaku Konjac. ” Current AI translators, including DeepL, Google, and ChatGPT, are available easily through the internet. It would be as if Doraemon's translator did a time-slip from the 22nd century into the modern world. A reader may use an AI translator for writing technical English papers. Before the advent of the AI translators, anyone had consulted with both English-Japanese and Japanese-English dictionaries to find unknown or unclear words, understand their meanings, and learn how to use them by referring to example sentences. Japanese is much more ambiguous than English in terms of bidirectional translation between these two languages. Haiku is one of the shortest poems in the world. It is compliant to a strict writing format, including a seasonal Japanese word. However, this form does not need to accurately convey the intentions of the writer to a reader, thus resulting in being open to multiple interpretations. In contrast, any technical paper written in any language must accurately convey the claims and/or thoughts of the author to a reader without misunderstanding. Thus, Japanese authors should write their technical Japanese papers clearly, concisely, consistently, correctly, and simple before using AI translators. They should subsequently check, proofread and revise their English-translated versions because any AI translator based on reasoning from context cannot avoid mistranslation. This article may look like, not a paper, but an essay. It describes how to make the best use of AI translators, including its hints and tips, based on the long-term experiences of the author in the field of power electronics.

Currently, hybrid railway vehicles utilizing fuel cells (FCs) and lithium-ion batteries (LiBs) are being studied as a means to reduce the environmental impact of non-electrified lines in rural areas. However, in this system, the relationship between load profile, FC power, and LiB energy capacity remains unclear. This paper proposes a method to determine the installed FC power and LiB energy capacity from the loss energy characteristics according to the line profile. The proposed method determines the required power supply capacity without the need to repeat a simulation.

In DC electric railway systems, energy-saving can be expected by using regenerative brake. However, since the regenerative brake force decreases at high-speed range, the use of a mechanical brake to obtain a constant brake force results in losses and reduces the energy-saving effect. The “regenerative brake notch”, brake method proposed in a previous study, suggests a way of informing the brake start point for stopping only with the regenerative brake force. However, when this method is applied to an actual train running, it is not always possible to stop at the stopping position due to disturbances such as the running resistance and the gradient of railways. In this study, we proposed a driver advisory system and a control method to solve this problem. We verified the responsivity of this control method in actual motors drive system and the energy-saving effects on applying the proposed method by using a numerical simulation assuming of an actual railway running.

To study security at facilities, particularly the capture of a suspicious person using only security robots, we investigated the pursuit problem. Multi-agent reinforcement learning has frequently been applied to this problem, in which multiple hunters catch single or multiple preys. In the pursuit problem, hunters are typically considered to have an infinite field of view (FoV) range to obtain the absolute or relative positions of the preys as the states of the hunters. However, this is inappropriate owing to “the curse of dimensionality,” and the FoV range should be restricted suitably. Moreover, strict restrictions on the FoV range prevent hunters from observing their states and continuing learning because they cannot obtain the position of a prey when it is outside their FoV. In previous studies, when a prey is out of the FoV of the hunters, they act randomly. However, in this study, we developed methods to allow hunters to continue learning when a prey is outside their FoV. In addition, numerical simulations were performed to evaluate the effectiveness of each method. The simulation results validated the effectiveness of developed methods from the viewpoints of learning performance and application of the learning results.

The dynamic eccentricity of rotors is a significant obstacle in their manufacturing process. This obstacle causes an imbalanced electromagnetic force and generates unexpected vibrations and acoustic noise. In this study, the effects of dynamic eccentricity on the temporal and spatial harmonic distributions of gap magnetic flux density and electromagnetic force are investigated, and the cause of the vibration is identified. Moreover, a compensation method is proposed to suppress the vibrations due to dynamic eccentricity by using a multi-sector and multi-phase motor. The compensation current is obtained by optimization. The effectiveness of the proposed method is verified by finite element analysis and experiments.

This study proposes a maintaining a quadrotor's attitude system using a ‘moment disturbance observer’ aimed at enhancing stability. In recent years, quadrotors have become increasingly prevalent in sectors such as agriculture, surveying, logistics, aerial photography, infrastructure inspection, and security. However, with their growing, there have been concerns about potential physical and human harm stemming from accidents. The Ministry of Land, Infrastructure, Transport, and Tourism has reported accidents attributed to challenging maneuvering conditions that have resulted in crashes. This study aims to develop a quadrotor that can maintain a stable attitude during sudden and significant alterations in its orientation. We suggest employing a moment disturbance observer to estimate the necessary moments for stable attitude maintenance. Numerical simulation results show that the proposed method surpasses traditional PID control in terms of attitude stabilization. Furthermore, this method resulted in superior attitude stability in single-axis experiments with a mechanically constrained quadrotor compared to conventional PID control methods.

It is widely known that switching characteristics are affected by parasitic parameters, i.e., stray inductance and capacitance, present in the main circuit of voltage source inverters. In this study, the influence of stray capacitance on the switching characteristics is investigated based on a switching model of a half-bridge inverter that incorporates both stray inductance and capacitance. We constructed two prototype inverters having different stray capacitances. The experimental results show that additional stray capacitance increases switching loss.

In sensorless control of variable magnetomotive force motor with a wide variable range, the variable magnetic flux changes and the magnetizing current becomes a disturbance, making the control system unstable. This paper proposes a control composition that detects the variable magnetic flux online using a magnetic flux estimator and provides the estimated magnetic flux of the permanent magnet as feedback to the controller. The magnetization characteristics of the variable magnetomotive force motor and the accuracy of the magnetic flux estimator are reported. It is shown that the controller becomes unstable when a value different from the true value of the magnetic flux is applied during sensorless control, and the usefulness of the proposed method is reported.

A three-phase inverter with neutral-line voltage injection is proposed to improve the output voltage waveform. This inverter consists of a three-phase inverter and a single-phase inverter. The former is referred to as the main inverter, which operates in the 120° conduction mode, and the latter is called the auxiliary inverter, which serves as a wave shaper injecting voltages of three-time and higher-order frequencies (odd triples) of the main frequency with PWM operation. The main inverter converts almost all the input DC power to AC power in the discontinuous rectangular waveform. The auxiliary inverter is applied to lower the total harmonic distortion (THD) of the output voltage. The design of the proposed inverter is presented in this paper. A digital-signal-processor (DSP) is used as a controller. The performance of the entire inverter is investigated in both theoretically and experimentally. The output three-phase voltages had a THD of approximately 4.3% in the experiment. The practicability of the control method is confirmed.

This paper presents a control method for the failure of one of the two units of a double three-phase-wound permanent magnet synchronous machine drive system without contact between these two units by estimating the state of the other unit based on magnetic coupling of a dual resolver. This paper proposes an another unit state estimation algorithm, in which the second unit extracts coupling signals from the output windings of the dual resolver. If the level of the extracted signals is smaller than threshold value, the first unit is determined to have failed. Experiments were conducted and the results showed the effectiveness of the proposed method.

This study aimed to develop a power supply system without a traction transformer for weight reduction and downsizing. Transformer-less power supply is expected to realize step-down, rectification, isolation, and motor drive using a high-voltage silicon carbide power device. The primary challenge of this study was developing a novel circuit that isolates the motor drive circuit from the AC line without using the traction transformer. Accordingly, we devised a flying capacitor circuit to solve the existing problems and achieve capacitive isolation. Subsequently, we devised a nesting capacitor as a short-circuit prevention measure. In this study, the operation of the isolated circuit was verified by numerical simulation, complemented by experimental verification of the proposed circuit.

D-systems, which inherently possess the ability to separate positive and negative phase components, are used in many applications such as flux estimation, back EMF estimation, current control, and harmonic disturbance suppression. D-systems are realized using inverse D-matrices. To implement a D-system in a discrete-time manner, the discrete-time realization of the inverse D-matrix is essential. This paper proposes a novel discrete-time realization of the inverse D-matrix, which is minimum order and have a compensation function for frequency characteristic changes caused by time discretization.

A high-accuracy magnetization process of permanent magnets (PMs) is desirable for manufacturing a high-performance PM synchronous motor (PMSM). Therefore, estimating the PM magnetization on a manufacturing process is essential. After the post-assembly magnetization of a PM loaded on a PMSM, the no-load back electromotive force (EMF) is utilized for estimating the magnetization condition of the PM. However, the estimation involves comparing the no-load back EMF measured using reference PM. Therefore, the PM magnetization is indirectly estimated. In this letter, a direct estimation method of magnetization of the PM of a PMSM using a back EMF of the PMSM is proposed.

This article introduces Power Electronics Laboratory (PI: Assoc. Prof. Hidemine Obara) at Department of Electrical and Computer Engineering, Yokohama National University. Their research interest includes electric power conversion technologies using semiconductor power devices and their applications.